The invention relates to scintillation crystals. (The term "crystal" includes bodies which are used as scintillators; such bodies may be single crystal, polycrystalline, amorphous, etc.) More particularly, the invention relates to thick scintillation crystals, i.e. crystals which are sufficiently thick that a large fraction of radiation incident on the crystal loses all its energy in the crystal as a result of interactions with it. In practice, thick scintillation crystals are at least 1/4 to 3/8 inch thick when used in gamma cameras, and may be several inches thick when used for oil well logging, background monitoring, and other applications. Thin scintillation crystals have thicknesses on the order of hundreds of microns and are used for example in X-ray equipment.
Thick scintillation crystals are traditionally grown as large single crystals. This is slow and expensive. Furthermore, the growth process requires large and expensive furnaces, and substantial machining is required to cut and polish the rough scintillation crystal into an appropriate form for mounting and encapsulation.
Thick scintillation crystals have also been produced by evaporation of CsI(Na). The end product of this manufacturing process is a thick crystal with a needle-like polycrystalline structure. Crystals so produced are unusable for applications in which the incident radiation is gamma rays, because the crystals are not clear enough, have poor conversion efficiency, and poor energy resolution.
For applications requiring very thick crystals, optical clarity is an important characteristic, because the clearer is a scintillation crystal, the less attenuated is the scintillation light generated in it. To produce thick scintillation crystals with the required optical clarity, conventionally grown scintillation crystals have been required. This is highly expensive.
One object of the invention is to produce a thick scintillation crystal without requiring the large and expensive furnaces needed to produce grown crystals.
A further object is to provide a thick scintillation crystal which is optically clear enough for use in applications such as oil-well logging, etc.
Yet a further object is to provide a thick scintillation crystal which can be produced more cost effectively than known thick scintillation crystals.
Yet still another object is in general to improve over the prior art.